No sorry, I don't use encryption, but just unassigning the cache devices is safe, you do need to have some attention when re-assigning them back, you first need to start the array without any device assigned to the pool to make Unraid "forget" current cache config, then stop array, reassign all cache devices and start array, there can never be a warning like "all data on this device will be delete at array start", existing pool will be imported.